1. Field of the Invention
The present invention relates to an image processing apparatus for forming either images of the parts of an object or images of an object which are identical but different in color, and for combining the images into a wide high-resolution image of the object.
2. Description of the Related Art
Image processing apparatuses using a solid-state imaging device such as a CCD are generally used in electronic still cameras, video cameras, and the like. It is demanded that an image processing apparatus have a higher resolution, particularly so high a resolution that the apparatus may provide a wide image of an object. Also it is desired that the image processing apparatus have so high a resolution that it can form an image as wide as a panoramic image.
Two techniques are available for increasing the resolution of the image processing apparatus. The first technique is to use a solid-state imaging device with a sufficiently high resolution. The second technique is to use a plurality of solid-state imaging devices for obtaining images of parts of an object, respectively, and to combine the images into a single high-resolution image of the entire object.
More precisely, the first resolution-increasing technique is to use more pixels per unit area of the device chip. In other words, smaller pixels are arranged in a greater number in the unit area, thus increasing the pixel density of the imaging device.
The second resolution-increasing technique is classified into two types. The first-type technique comprises the first step of controlling the optical system incorporated in an image processing apparatus, thereby switching the view field of the apparatus from one part of an object to another part and thus enabling the imaging devices to produce images of parts of an object, and the second step of combining the images, thus produced, into a high-resolution image of the entire object. The second-type technique comprises the first step of dividing an optical image 600 of an object into, for example, four parts by means of prisms as shown in FIG. 1, the second step of applying the parts of the optical image to four imaging devices 611, 621, 631, and 641, respectively, and the third step of combining the image data items output by the devices, thereby forming a single image of the object. In the second-type technique, the imaging devices 611 to 641 are so positioned as to cover the predetermined parts of the object as illustrated in FIG. 2.
There is known another resolution-increasing technique similar to the second-type technique described in the preceding paragraph. This technique uses a detector 611 having four imaging devices 612 which are arranged in the same plane in a 2.times.2 matrix, spaced apart from one another for a predetermined distance as is shown in FIGS. 3A to 3C. The view-field image 613 of an object (i.e., a broken-line square) is intermittently moved with respect to the imaging-device matrix by driving an optical system, in the sequence indicated by FIGS. 3A, 3B, 3C, and 3D. The optical image of an object need not be divided by prisms or similar means, unlike in the second-type technique.
The conventional resolution-increasing techniques, described above, are disadvantageous in the following respects.
The first technique can increase the resolution but to a limited degree, for two reasons. First, the number of pixels the existing manufacturing technology can form in the unit area of the device chip is limited. Second, the smaller a pixel, the less sensitive it is. A larger device chip may indeed be used to form more pixels on the chip. With the conventional manufacturing method, however, the ratio of defective pixels to good ones will increase if many pixels are formed on a large chip. Consequently, solid-state imaging devices having a large image-receiving surface can hardly be manufactured with a sufficiently high yield.
In the second resolution-increasing technique, the image data items output from the imaging devices (e.g., four devices) are combined to produce a single image. To render the reproduced image substantially identical to the original image of the object, the images of the object parts should neither be spaced apart nor overlap one another. The images will be spaced apart or overlap unless the pixels arranged along that edge of one device which abut on the edge of the next device are spaced by exactly the one-pixel distance from the pixels arranged along that edge of the next device. The imaging devices therefore need to be positioned with very high precision during the manufacture of the image processing apparatus. It takes much time to position the devices so precisely, inevitably reducing the manufacture efficiency and, ultimately, raising the cost of the image processing apparatus.
Also in the resolution-increasing technique similar to the second-type technique, the imaging devices must be positioned with high precision. In addition, the optical system must be driven with high precision in order to intermittently move the view-field image of an object (i.e., a broken-line square) with respect to the imaging-device matrix. A high-precision drive is indispensable to the image processing apparatus. The use of the drive not only makes it difficult to miniaturize or lighten the apparatus, but also raises the manufacturing cost of the apparatus.
A color image processing apparatus is known, a typical example of which is a so-called "three-section color camera." This color camera comprises a color-component generating system and three imaging devices. The color-component generating system decomposes an input optical image of an object into a red image, a green image, and a blue image. The three imaging devices convert the red image, the green image, and the blue image into red signals, green signals, and blue signals--all being television signals of NTSC system or the like. The signals output from the three imaging devices are combined, whereby the red, green and blue images are combined, forming a single color image of the object. A color image with no color distortion cannot be formed unless the imaging devices are positioned or registered with high precision.
Images of parts of an object are combined, also in an image processing apparatus which has a plurality of optical imaging devices for photographing the parts of the object on photographic film, thereby forming a panoramic image of the object. To form a high-quality panoramic image, the images of the object parts should neither be spaced apart nor overlapping one another. Hence, the optical system incorporated in this image processing apparatus must be controlled with high precision. Consequently, the apparatus requires a complex device for controlling the optical system, and cannot be manufactured at low cost.